Antenna system for defining a blind approach path



Jan 27, 1948'. l.. J. HEAToN-ARMSTRONG 2,434,927

ANTENNA SYSTEM FOR DEFINING A BLIND APPROACH PATH- Filed oct. 15, 1943 s sheets-sheet 1 FIG. ra).

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A ttq y Jan. 27, 1948. L. J. HEAToN-ARMSTRQNG 2,434,927

ANTENNA SYSTEM FOR DEFINING A BLIND APPROACH PATH Filed oct. 15, 1943 s sheets-Sheet 2 /r/G.2(a).

Jan. 27, 1948. l.. J. HEAToN-ARMSTRONG ANTENNA SYSTEM FOR DEFINING A BLIND APPROACH PATH Filed OCl.. 15, 1943 3 Sheets-Sheet 5 A ttor Patented Jan. 27, 1948 ANTENNA SYSTEM FOR DEFINING A BLIND APPROACH PATH 'Louis John' 'Heaton-Armstrong; cLondon, Eng- 1 "lland; assgnor, by mesneassignmentsfto International Standard Electric Corporation, New York,.NL'5E;.fa-corporation ofiDelaware Application October 115, 1943,.S,lial No. 4506,301 `In `(Sweat Britain NovemberV I0, 1942 .SectonTfPublic-Law 690; fAugustgi-IMG. 4Patent yexpires November d0, 1962 5 Claims. Y (Cl. Z50-11) *Ihcpresent Ainvention Telatesfto azradiobeacon for :radio guiding systems "ofithe :kind 1n l,which a :neld :distributionffor sfleldfstrengthpattern is commutatedfor :keyed rsoV as -to :produce A minime-- 2 Asianomparison a .particular case is worked out 'for `a system accordingto the `invention-six wavelengths widewhich gives -a beam width `of .115 and the field strength -on the equi-signal mentary :signals lato"thenight fand `lett of tthe 5 line is .14.5 db. higher than that for the -3 fed course respectively, and on the course :.a-.continunA antenna system'rwith. aerial spacingof .475 waveousv Adash :Orino .'si'grialfand is an improvement :in length. or -fmodi'lcationrof theradiofbeacon fsystem-'de- Consider -three 4antennae A, B and C as .in scribed-nd1aimed'-1n our vmogliending British Figmla `fed .with .currents .in lphase relationship applicationfNo.1070.0/42. 10. 180, 90fand 0? as indicatedby the arrows.

Anfobiectzoffthainventioniato provideiasystem yIwv-e move round Ythe antenna .B and measure which will .'.produce :awnarrowergpatnaor. Ibeam thephase.andmagnitudefofthe field fromA and width rtharr is :obtainable by fthe. three ffedtan- C .we shall ffind that .the .resultant iield from A tenna farrangements described @and claimed 4in andwillfalways beeitherin .phase or 180 out (Junco-Pending Brtishabplication No.;10700/.4-2. 15 ofwphasewith. that vfrom antenna B. The `-eld The beamwidth mayfbe ydefined.astheangle substrength is shown in Fig. 1b for the antenna B tendediatithe antennarbvWO-.Dontsonelon either andg-for the .resultantof Aand C. The number sideofthaequifsgnalline whenethefratiofotthe of lobes produced by A and ,Gis determined'by nelds .fromthe.twa-.overlanpina patternsmas a the spacing .0f antennae `A--Bv and. B-C, two given,ratio,.usually takenasr5%. 20 complete .lobes .being produced 'by a spacing of ...According .toV .the 1present.. invention. a radio beacon of -thegkind..hereinbeore. speeinedmom.- prisesacentralfantenna ,andaeroup onantennae inpalignment on. each sideofsaidpentral antenna, the groups of antennae being `fed with currents Whose phases are ...orbnpositesiens (le'adingnr lagging.) .witnarespect ta .the current 'said centrallantenna.andmeans fior .reversing the .sign of lthe phase. .(from .lead l.to lag ^or'. .vice versa) of the .currentin the A:central antenna` with respect.tathecurrentsinthegroups.

Theinvention will lbe lbett'er. understod .from the fiollowingdesciption taken'in ,conjunction witnthe .accompanyingl-d1tawinga in which Eig. `la ,shows schematcallythe ithree fejd antennasytem Figs. 112,19, 1d (and 'learje iieldstrengtli Ydiagrams;

.Fig. 2a showsschematlcallyjjhe antennafsystem accordingto.thepresentinvention Eigs ;2 b ,and '2c are eld Nstrength V*diagrams correspondingjtdFi'gs; 1b and -iclbutiof thesystem sbownin EigrZc:

Figs. '3a v`andbarefteld strength diagrams of asystem according'ito the invention-1in Awhich the current inthe two #antennae adjacent tthe central antenna lis 4I,`*that `i'rrjlie* -central antenna 101 and jhatin 'each "of (thefcther antennae is-I.; and

1g. 41shows diagrammatically afsuiftableikeying unit;v

11n. order to'bring Aout-the'"-inventio n` clearly -a comparison' of a system according tti-the invention will .be made withthe'threefantennasystem of application'Na10700742.

.25 wavelengthasshown at Fig. 1b. Fig. lo shows theresultantleld strength diagramfor the .three antennae, the fields being added in curve l. In

curve?! .thegphase oflband Chas been changed by 180. These are the two well-known over'- lapping .eldpatternswhich give an equi-signal path-...at 0.",andY 180 as shown, butthe width of the beam is not ,as small as desired.

Figs. 1d and 1e show the similar curves but with a spacing. between the antennae of more than one wavelength. :It .will be seen that there are ten equi-signal paths altogether (the same number as the number of lobes). Note also that each alternative lobe is of reversed phase and it is this reversal of .phase .that vcauses the unwanted equi-signal paths. Hence whilst a narrowerwbeam may -be obtainable :byincreasing the spacing between the antennae, false paths :are introduced. y

Consider now an antenna system comprising two groups of antenna AI A12 and CI CIZ fed"180` out of phase and Va vcentral lantenna 1B fed at as shown in Fig. 2a.

If we proceed round thsantenna .system Vwe shall nd that the lobes adjacent to 0 and '180 are larger than any others and that the lobes oi reversed :sign to these Ylarge lobes are much smaller and if the number of antennae 'n inA each group is very Alarge .and d/l. is small where d is the distance between two .adjacent fantennae and lv the operating wavelength, these lobes \will become vanishingly small.

This condition can be seen vectorially in Figs. 2b vand 2c. Figi2b shows the eld vectors starting 'to `close in and their resultant `is "OY which will have a small resultant as shown at OQ which J is in reverse phase to OY (Fig. 2b)

By increasing the current in the aerials AI and CI adjacent to the centre one B, the resultant can be made always to have the same sign, so

that there are no negative lobes and therefore A particular case'forv n=12,

no false courses. d/A=1A is shown in Figs. 3A and 3B. Here the aerial currents are in the following relative values, for the central antenna B, 4 for the two aerials AICI adjacent to B, and 1 for the remainderv A2-I2 and C2-I2. In Fig. 3a, curve I Vis the curve of eld strength distribution due to the centre antenna B, and is linear. field strength distribution due to additional current strength in the antennae AICI adjacent the central antenna and curve 3 shows the iield strength distribution due to the groups of antennae all with equal currents.

In Fig 3b the continuous line curve shows the sum of the curves I, 2 and 3 of Fig. 3a; the broken line curve shows the difference between the sum of curves 2 and 3 of Fig. 3a and of curve I, (i. e., 2-I-3-1 it being assumed that the phase of eld represented by curve I is reversed).

The line of intersection OX of these two iield distribution curves in Fig. 3b then defines the desired course, and it will be observed that these curves cross each other at only one point, namely, on the line OX, and thus no false courses are dened.

The antenna system may be treated mathematically as follows: Y

1. Take eld pattern as centred on B, and of phase corresponding to the field set up by an aerial at B energised with the reference phase c.

2. Consider the antennae other than B as operating in pairs AI-CI, A2-C2, A3-C3, etc. An-Cn spaced apart 2nd and having equal currents.

3. The field set up in the direction o to the antenna alignment by any pair of aerials will be the sum of two vectors, of equal amplitudes, but of phases (rt-him sin 0) and (180-s+2r7fd sin o) giving a resultant of phase (4a-90) and amplitude 2K1 sin 21rnd sin 0 Where K is a constant for any particular distance.

4. The eld produced by all the antennae is thus 2K1 sin2%d sin IWI-sin? sin 0+ sin2nrdsin 0 sin gg sin 0.sin n--M sin 0 Curve 2 shows the 4 is nearly always positive a typical example being shown in Fig. 3a curve 3 in fullline.

If now the currents in the two antennae AI-CI adjacent to the central antenna B are increased duced by the two groups of antennae is sin "i sin @.sin sin 6 l; sin 0 By choosing I1 suii'ciently large the above expression will not change sign between 6=0 and 180'and between 180 and 360 and no false courses will therefore be obtained.

Less than 180 phase change may be used for keying if preferred thus simplifying the keying problem, by requiring only a single contact-keying device. If, for example 90 phase change is used the phase of the antenna currents in this case will be 0 45 180 for outer group, central antenna and outer group. On keying the'phase of the central antenna B would bechanged to 315. In the case utilising dipole antennae keying is electecl by shunting a reactance across the central dipole B.

All the antennae may be fed from the same source, from a common junction point Yin a transmission cable and the length of the line from the said junction point to the central antenna B is made an odd number of quarter wavelengths of the operating frequency, and the lines to the sin other' antennae have corresponding electrical lengths with respect to the antenna spacing and desired phase of the currents in the antennae. Then since the length of line to the central antenna is an odd number of quarter wavelengths long, the effect oi. the reactance across the central dipole is to change the phase of the current fed to that dipole. By using a reactance equal in magnitude to the antenna resistance, and by changing the reactance from capacitive to inductive and vice versa, aphase change of 90 is obtained whilst obtainingU a constant current in the antenna. Y Y

A suitable keying unit is shown in Fig. 4. This unit comprises an adjustable inductive loop L4 of, for example '70 ohms impedance and a capacity C5 of 140 ohms impedance which is placed in series with the inductance. The relay RELI when operated short circuits the condenser C5 by closing the make contact rI. This converts the impedance across the dipole from '70 ohms capacitive reactance to 'l0 ohms inductive reactance. C6 is a blocking condenser to prevent the relay short circuiting its operating current. L5 is a choke coil to keep the radio frequency energy from the relay winding W.

The transmitter T feeds a line TD by means of the transformer TR having tuned primary and secondary windings. LI, C3 is a circuit for suppressing parallel currents on the line TD: capacities CI, C2 and C4 and inductances L2. L3 form a network for feeding the operating current from supply S to the relay RELI along the line, thus eliminating the requirement oi a separate cable. The keying mechanism is represented as a'key K, and connects the source S to the line TD through Y the inductances L2, L3. 'I'he key K may of course be any suitable switching device, for example, mechanical, electromagnetic or electronic, well known in the art, and in normal cases would be automatically operated.

Whilst a specific embodiment of the invention has been described by way of example, other embodiments of the invention will occur to those skilled in the art and which fall within the scope of the appended claims. For example, the phase of the currents in the groups of antennae may be changed and the phase of the current in the central antenna would then be kept constant.

What is claimed is:

1. A beacon for radio-guiding systems of the type in which eld distribution of pattern is commutated, so as to produce complementary signals to the right and left of the course respectively and to produce on the course a continuous signal, including a central antenna and other groups of antennae located in alignment on each side ,of said central antenna, means for feeding the respective groups of antennae with currents the phases of which are of opposite signs with respect to the current in said central antenna, means for reversing the sign of the phase of the current in said central antenna with respect to the currents in said other groups, and means for making the strength of the currents in the antennae of said groups nearer said central antenna relatively greater than in the other antennae of said groups, and of such energy value as to eliminate any reversal in sign of the eld distribution around the system.

2. A radio beacon as claimed in claim l, including additional means for causing the phase angle of the current in said central antenna to be at 45 with respect to the current in one of said outer antenna groups and means for changing said phase angle by 90 so as to change said phase angle from a lead t0 a lag and vice versa.

3. A radio beacon guiding system of the type employing phase reversal of at least one antenna of a plurality thereof, wherein said antennae are dipoles and there are included means comprising an inductance of the same impedance magnitude Ias the resistance of the center dipole and a capacitor connected in series therewith and having a capacity of twice said impedance magnitude, said inductance being connected in shunt across the center dipole and wherein there are provided further means for alternately short circuitng said capacitor, so as to render the said dipole alternately capacitative and inductive, thereby causing the phase angle of the current in said lcentral antenna to be at with respect to the current in one of said outer antenna groups and to change by upon operation of said short circuiting means.

4. A radio beacon as claimed in claim 3, wherein said short circuiting means comprises a single make and break contact relay.

5. A radio beacon as claimed in claim 3, including also a line feeding to the center dipole current to be radiated, an electromagnet for operating said short circuiting means and located at said dipole, and means for feeding exciting and controlling current to said electromagnet over said dipole feeding line.

LOUIS JOHN HEATON-ARMSTRONG.

REFERENCES CITED The following references are of record in the 

